Lecture 31: Skeletal Muscle Part II Flashcards
What is length-tension relationship?
For an isometric contraction -> in which in which the length of the muscle does not change, maximum active force (tension developed) changes with the resting sarcomere length of the muscle
Why does the length of sarcomere affect the maximum active force (tension developed)?
Degree of actin and myosin overlap changes with resting sarcomere length
At what lengths can maximal force be produced?
2.0 - 2.2 micrometers
What happens as the resting length of sarcomere becomes too long?
Maximum active force degrees at steady rate as degree of overlap between myosin and actin decreases
What happens as the resting length of sarcomere becomes too short?
Filaments collide and interfere with each other reducing the amount of force that can be developed
What is passive force?
The force produced due to elastic component of muscles -> as muscle is stretched connective elements resist this extension = passive force
How do you work out total tension?
Sum of active tension (determined by length of sarcomere) and passive tension
What is the relationship between active force and passive force?
Active force increases as muscles contract - length decreases -> this leads to the increase of passive force as connective elements resist extension to greater extent
What is a motor-unit?
A motor-unit consists of a single motor neuron and all the muscle fibers it innervates
What are the two parts to excitation-contraction coupling?
1: Neuromusclar junction
2: Calcium coupling
Explain the calcium coupling stage of excitation-contraction coupling?
Action potential is conducted down t-tubules (in contact with sarcoplasmic reticulum opening)
Voltage-gated calcium channels in the sarcoplasmic reticulum open allowing calcium ions to diffuse into the cytosol of the muscle fibre
How does muscle contraction end?
Muscle contraction ends when calcium ions are actively pumped back into the sarcoplasmic reticulum by calcium ion pumps
What are the sources of ATP for muscle metabolism?
- Creatine phosphate
- Anaerobic glycolysis
- Aerobic metabolism
Describe how energy is obtained from creatine phosphate
Creatine phosphate + ADP = creatine + ATP
Creatine phosphate is therefore an anaerobic source of energy (no oxygen required) and quickly spent <15s
Used for short bursts of energy
Describe how energy is obtained from anaerobic glycolysis
Energy obtained without the use of oxygen from glucoe
Fast but inefficent as only 2 ATP per glucose
Used for 10-30s of maximal effort
Build up of protons limits anaerobic glycolysis as enzymes cannot function under highly acidic conditions
Describe how energy is obtained via aerobic respiration?
32 ATP per glucose -> efficient
Requires oxygen -> good blood supply
Required for postural muscles and endurance exercises
What are the two types of muscle fibres?
Type 1 (slow oxidative) Type 2 (fast glycolytic)
What are type 1 motor units?
Units with neurons innervating the slow efficient aerobic cells (maintain posture and walking)
What are type 2 motor units?
Units with neurons innervating the large fibres that fatigue rapidly but develop large forces (jumping, weight lifting)
How is force produced by muscles regulated?
1) Rate of stimulation of individual motor units
2) Total number of motor units recruited
How does increased rate of stimulation increase force produced?
Temporal summation -> as increased frequency of stimulation occurs muscles do not relax between stimuli
How does total number of motor units regulate force of muscles?
As more units are recruited tension increases
Fatigue resistance motor units are recruited first
